Traditional network architectures, defined legacy networks, are based on a centralized network Manager controlling each network element; the Manager can be connected directly to the managed network element or indirectly through channels carrying control data in the same physical network carrying user data or through a different physical network carrying only control data. The centralized Manager is a software application running on a management station and performing network management functions and it is responsible for configuration of the connections, monitoring alarms and performance of the connections, for protecting the connections providing a backup connection in case of a fault on a segment of a nominal connection. The disadvantage of this architecture is that the centralized Manager can't manage network elements of different vendors unless a previous vendor agreement on management interfaces is reached. The centralized Manager performs the management functions according to the model Manager—agent—MIB. MIB stands for Management Information Base and it is a hierarchical data structure stored into each network element or into the management station defining groups and objects in the groups, the objects including variables for managing the network element; for example, a variable stores the number of bytes received from a network interface. For a TCP/IP-based network the second version of MIB is defined in RFC2011 and RFC2012. The centralized Manager sends and receives messages to MIB of a network element according to a management protocol, like SNMP, Qx, Q3 or Qecc, for performing reading and writing operations of the variables of the MIB and consequently for reading and changing the status of the network element. The agent is a software process running on a microprocessor of each managed network element and performs the translation of messages between the Manager and MIB. The advantage of this architecture is a standard management protocol between the Manager and the agent and a standard data structure of MIB, while the Manager and the agent is specific for each network element which can belong to different vendors.
The new network architectures are based on a distributed Control Plane (CP), like defined in ITU-T G.8080/Y.1304 for the Automatically Switched Optical Network (ASON), in addition to the usual Transport Plane (composed by the network elements described above) and centralized Management Plane (MP). The Control Plane is composed by Control Plane Elements (CPEs) interconnected each other and one CPE controls one or more Transport Plane Elements (TPEs). FIGS. 1 and 2 show schematically in Manager B domain the TPEs and CPEs of the ASON architecture, wherein each TPE has a correspondent CPE. Manager A and Manager C are the MP for domain B; moreover Manager A is the centralized Manager for domain A and Manager C is the centralized Manager for domain C. In the ASON architecture a new connection can be requested by the MP (and it is defined SPC, that is Soft Permanent Connection) or by the customer (and it is defined SC, that is Switched Connection) through User Network Interface (UNI); the request is sent to the CPE of the ingress end point of the connection and the connection is set up through a signalling protocol between the CPEs. Various signalling protocols can fit the ASON architecture, like RSVP-TE (RFC3209 and ITU-T G.7713.2), CR-LDP (ITU-T G.7713.3, RFC3472), PNNI (ITU-T G.7713.1) and OSPF-TE (RFC3630). The advantage of ASON architecture is that are defined standard interfaces (between two CPEs, between a CPE and a TPE, between MP and CPE, between MP and TPE) and it is possible to manage network elements of different vendors. A further advantage is that the Control Plane is responsible to provide a fast and efficient configuration of new connections within the Transport Plane, modify the connections previously set up and perform a faster restoration function providing backup connections for protecting the nominal connections.
Network operators have already deployed network architectures with a centralized network Manager and are changing part of the network (or deploying new networks) to the ASON architecture, so that both architectures coexist. In this scenario at least one resource is shared between the centralized Manager and the Control Plane Element; the shared resource can be for example a link (i.e. an electrical cable or an optical fibre) between two network elements of two different network domains or part of the one network element between two different network domain. For one network element the shared resource is for example a matrix or one or more ports connected to the matrix. Referring as an example to FIG. 1 and FIG. 2, in FIG. 1 link A-B is shared between Manager A (central Manager for domain A and MP for domain B) and distributed Manager B (CPE for domain B), while link B-C is shared between distributed Manager B (CPE for domain B) and Manager C (central Manager for domain C and MP for domain B); in FIG. 2 network element indicated with NE1 includes a matrix shared between Manager A (central Manager for domain A and MP for domain B) and distributed Manager B. The problem of sharing resources arises not only with the introduction of the ASON architecture, but also in traditional networks, wherein a resource can be shared between two centralized Managers. Still referring to FIG. 1 and FIG. 2, in FIG. 1 link A-C is shared between centralized Manager A and centralized Manager C, while in FIG. 2 network element indicated with NE2 is shared between Centralized Manager A and Centralized Manager C and also with distributed Manager B.
Management of shared resources is required for controlling network management functions and in particular for provisioning and protecting connections between different domains crossing the shared resource; these connections are indicated with c1 and c2 in FIG. 1 and with c3 and c4 in FIG. 2. For a shared link, that is a segment of a connection, the solution can be to assign statically in advance the link to one Manager, so that only this Manager can use this link for controlling the connections. This is shown in FIG. 3, which includes more details of network elements NE3 and NE4 of FIG. 1. Each network element includes a connection matrix (connection matrix NE3, connection matrix NE4) having connection points for performing cross-connections within the matrix by connecting different connection points and includes ports (P5, P6, P7, P8) for connecting a group of connection points to a link, the link connecting different network elements. The bandwidth of the link of one port is at least the sum of the bandwidth of the connection points of the port. The port also includes means for performing management functions of the correspondent connection points, such as fault and performance monitoring. The shared resource is link A-B connecting one port of NE3 in domain A to one port of NE4 in domain B. According to this solution, link A-B is assigned for example to Manager A, which is responsible to control this link for providing connections between the two domains; this is a disadvantage because Manager B can't use this link also if it is not used by Manager A.
For a network element including a shared resource, the problem is to control the segment of the connection inside the network element crossing different domains. FIG. 4 shows more in detail network element NE1 of FIG. 2 including some ports (P1, P2, P3, P4) and a connection matrix having connection points (cp11, cp12, cp31). The cross-connection within the matrix indicated with c13 in FIG. 4 is a segment of connection c3 of FIG. 2; this segment internal to NE1 is required for connecting for example connection point cp12 of port P1 to connection point cp13 of port P3 crossing the two domains. In this case the solution can be to demand to the control system of the network element the responsibility of the management of the shared resource for providing the segment c13 of connection c3. Referring to FIGS. 4 and 5, ports P1 and P2 (and the correspondent connection points) are controlled by Manager A, while ports P3 and P4 (and the correspondent connection points) by Manager B. The matrix is logically divided into two sub-matrixes A and B, as shown in FIG. 5: the first one is controlled by Manager A and the second by Manager B. Two virtual ports, VP1 and VP3, are created respectively for port P1 and P3 and a logical link Ic3 connects the two virtual ports. The first virtual port VP1 is connected to sub-matrix A and is controlled by Manager A, while the second virtual port VP3 is connected to sub-matrix B and is controlled by Manager B. When c13 is required, input cp12 from port P1 of the first sub-matrix must be connected to output cp13 of port P3 of the second sub-matrix, crossing Idc3. Manager A controls the connection Ic12 from input cp12 on port P1 to logical output Icp11 on port VP1 of the first sub-matrix, Manager B controls the connection Ic33 from logical input Icp31 on port VP3 to output cp13 on port P3 of the second sub-matrix and the connection from output Icp11 of the first sub-matrix on port VP1 to input Icp31 of the second sub-matrix on port VP3 is already provisioned by the control system of the network elememt NE1 using Ic13. In this solution some resources (VP1, Ic13, VP3) are used to carry connections crossing the two domains and can't be used for carrying connections in the same domain. The logical sub-matrix can have a physical correspondence to the connection matrix. For example, the connection matrix can be composed by a three-stage architecture: the first one is assigned to sub-matrix A controlled by Manager A, the third to sub-matrix B controlled by Manager B and some resources of the second stage are controlled by the local control system of the network element for performing the virtual ports and the logical links. Since the control system of a network element is local to the network element, it has not a global view of the network: this solution has the disadvantage not to find the best configuration of the connections in the network or of segment connections within the matrix and sometimes this solution can't even fit the network requirements. Moreover this solution adds an unnecessary complexity to the network element and reduces network element performance. Finally it has impact on implementation of the network element and the introduction of the Control Plane requires a change also of network elements, i.e. of TPEs.
Each Manager controls both the configuration of the logical sub-matrix of the correspondent domain and other management functionalities related to the connections of the controlled domain.